Testing the Paradigm that Ultraluminous X-Ray Sources as a Class Represent Accreting Intermediate-Mass Black Holes

摘要: To test the idea that ultraluminous X-ray sources (ULXs) in external galaxies represent a class of accreting intermediate-mass black holes (IMBHs), we have undertaken program to identify ULXs and lower luminosity comparison sample with highest quality data Chandra archive. We establish as general property most X-ray-luminous objects possess flattest spectra (in bandpass). No prior studies established hardening ULX luminosity. This occurs at highestluminosities (absorbed � 5 ; 10 39 ergs 1 ) isin line withrecent modelsarguingthat are actually stellar mass holes. From spectral modeling, show evidence originally taken mean IMBHs—i.e., ‘‘simple IMBH model’’—is nowhere near compelling when large is looked properly. During last couple years,XMM-Newtonspectroscopy has extent begun negate simple model based on fewer objects. confirm expand these results, which validates XMM-Newton work broader sense independent data. find (1) cool-disk components present withroughlyequalprobabilityandtotalfluxfractionforanygivenULX,regardlessof luminosity,and(2)cool-diskcomponentsextendbelowthestandardULXluminositycutoff ,downtooursamplelimitof 38.3 .The